A 106.1dB DR, 450μA Idle Current Class-H Piezoelectric MEMS MicroSpeaker Driver with Envelope Tracking, Digital and Analog Inputs and Less Than 2.1μs Latency

Piezoelectric transducers are widely used as audio, vibration, or mechanical actuators in a variety of applications, from consumer to biomedical, to automotive and industrial. Due to their capacitive nature, they can be extremely energy efficient, but they need to be driven at higher voltages compared to non-piezoelectric transducers. MEMS Micro-Speakers (MMSs) are a special class of piezoelectric transducers, used to reproduce audio for portable applications such as True Wireless Stereo (TWS), Over-ear Wireless Stereo (OWS), smart glasses, or similar wearable products. MMSs offer many advantages compared to traditional loudspeakers, such as small size, high efficiency, scalability and repeatability, and best in class sound quality. Consumer earphones, as well as hearing aid products based on MMSs are starting to be commercialized. The challenge in adopting MMSs in wearable applications is to design a driver capable of delivering audio signals with amplitude up to 30V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</inf> and additionally supplying a 5V to 15V DC voltage (V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</inf>) to bias the MMS membrane, avoiding negative voltages across it. The system is normally powered from a single Li-lon cell battery with limited capacity, thus requiring ultra-low power consumption and limited peak currents in all modes of operation. Another important MMS driver requirement is to minimize the latency of the signal path (<3μs), to enhance the performance of the ambient noise cancellation algorithms, which are a must in wearable audio devices.